The present invention relates to an optical disk read/write apparatus and a writing method, and more particularly to a technique applied to Running Optimum Power Control (ROPC). ROPC controls a semiconductor laser to obtain optimum laser power while writing to a writable optical disk to prevent the ROPC from becoming uncontrollable due to the influence of the tilt of the optical disk. The technique detects an inappropriate tilt angle based on the optical power of the laser used by the ROPC and performs tilt control before resuming the ROPC operation.
When writing data on a writable optical disk such as a CD-R using a laser beam, a trial write operation is performed on the power calibration area (PCA) provided for trial write operations on the inner circumferential side of the lead-in area of each optical disk. Here, comprehensive evaluations check the influence of variations in sensitivity of the optical disk, in laser characteristics of the optical pickup, in precision of the lens assembly, and in write speed.
In the trial write operation (power calibration), test data is written while changing the write speed and the write power of the laser in a stepwise manner. When the test data is read, the asymmetry (β) between the signals from the pit portions and the groove portions is evaluated, and write power exhibiting a good asymmetry level is designated as optimum writing power.
During the actual write operation, the write laser power is controlled to be at optimum power level, thereby optimizing the asymmetry of the reflected light (write pulse signals) from the optical disk, to accommodate variations in the optimum write power due to fluctuations in the sensitivity of the optical disk, shifts in the laser wavelength attributed to temperature changes, changes in the tilt of the optical disk, etc. This control operation is referred to as Running Optimum Power Control (ROPC).
FIGS. 4(a) and 4(b) are characteristic curves of the amount of received light reflected from an optical disk and the write laser power, respectively. FIG. 4(a) shows changes in the amount of received light over time, while FIG. 4(b) shows changes in the write laser power over time. When laser power as shown in FIG. 4(b) is used to irradiate laser light to a writable optical disk in a write operation, the amount of reflected light received changes as shown in FIG. 4(a) in the write operation. In the figure, characteristic curve 41 represents the amount of light received with an appropriate write laser power level. Characteristic curve 42 represents the amount of light received with an insufficient write laser power level; and characteristic curve 43 represents the amount of light received when the write laser power is too great. As can be seen from these characteristic curves, the output (B level) at point B decreases with increasing write power and increases as the write power decreases. The asymmetry of each signal at point B is evaluated to optimize the write power.
Conventional tilt control methods in which the tilt of an optical disk is corrected by use of a tilt sensor, have historically had the problem of being unable to control the tilt during write operation. For example, one technique has been disclosed in which returned laser light reflected from the optical disk is photoelectrically converted into an RF signal by a photoreceptor. The signal is used to adjust the tilt of the optical disk during a write operation (see page 1 of Japanese Patent Laid-Open 2001-184689).
Further, an increasing number of optical disk devices have been applied to portable equipment. In the case where an optical disk device is incorporated in a camera, for example, a large and instantaneous change in the tilt of the optical disk occurs due to the Coriolis force when the camera is panned, and this state can be sensed. A technique using this change has been disclosed in which a circuit for determining the total amount of light on the photoreceptor within the optical pickup is provided to control the write operation to the optical disk (see page 3 of Japanese Patent Laid-Open No. 2002-74671).